This invention relates to implantable biomedical devices, such as intraocular lenses (IOLs), and to methods for producing such devices. More particularly, in one aspect, the present invention relates to relatively straightforward and easy to practice methods for producing IOLs, and to such IOLs wherein the optics and haptics are integrally formed of the same material.
The use of IOLs to improve vision and/or to replace damaged or diseased natural lenses in human eyes, particularly natural lenses impaired by cataracts, has achieved wide acceptance. Accordingly, a variety of IOLs have been developed for surgical implantation in the posterior or interior chambers of the eye according to a patient's needs.
Known IOLs comprise an optical lens portion, or optic for short, which includes an optical zone, and one or more, preferably two, supporting structures called fixation members, or haptics for short, for contacting eye tissue to fix or hold the IOL in the proper position after implantation into the eye. The optic may comprise a soft, resilient material, such as a silicone polymeric material or a relatively hard or rigid material such as, for example, polymethylmethacrylate (PMMA). The haptics typically comprise a filament constructed of a resilient metal or polymeric substance, such as PMMA, polyimide or polypropylene.
Each of the filament haptics is preferably flexible to reduce trauma to sensitive eye structures and to be yielding during insertion of the IOL. In addition filament haptics generally have a memory retaining capability, e.g., springiness, so that after implantation of an association IOL, the filament haptic automatically tend to return to their normal orientation.
As an alternative to filament haptics, some IOLs are provided with footplate-type haptics. These footplates generally extend radially outwardly from the optic in the plane of the optic, and terminate in rounded or blunted end configured for placement in an eye chamber. The material for such footplates have included soft materials, for example silicone or 2-hydroxyethyl methacrylate (HEMA). However, footplate-type haptics are attended by disadvantages, such as the addition of extra material weight to the IOL and reduced flexibility, as compared to filament haptics, leading to poor fixation and consequent migration or dislocation of the IOL.
Although the filament haptics are generally preferred over the footplate-type haptics for several reasons, certain difficulties remain. For example, filament haptics and soft or deformable optics tend to be formed from dissimilar materials which do not ordinarily chemically bond together. As a result, filament haptics have been designed having a variety of attachment end configurations or structures. For example, anchor structures that provide a physical or mechanical interlock between the haptic and optic are used. Polypropylene haptics, for example, have heretofore been secured into silicone polymer-based optics by means of a mechanical lock and other means that require complicated manufacturing steps to produce. These means include pouring a pre-cursor material for the optic into a mold in which the haptic has already been placed, and then curing the optic around the proximal end of the haptic. Another means is to drill a hole into a pre-formed optic and then chemically or otherwise enhance the bond between the optic and the end of the filament haptic inserted into the drilled hole in the optic.
While procedures such as these can be effective for enhancing the haptic/optic bond strength, they may be relatively sophisticated and relatively expensive to practice. In addition, substantial care must be exercised in some of these manufacturing processes due to the extremely low tolerances of the materials to process and material variabilities. Moreover, even though these procedures can produce a bond between the haptic and optic sufficiently secure for purposes while the IOL is implanted within the eye, quite often the handling of the IOL prior to inserting it into the eye can subject the haptic to greater forces.
Therefore, it would be advantageous to provide a relatively straightforward and easy to practice method of producing IOLs which have substantial pull strength between the haptics and the optic. One easy way to accomplish this is to integrally form the optic and haptics in a single molding step, in which case, the haptics would be the same material as the optic. Because the optic is required to be made from a biologically inert and optically transparent material, such as polymeric silicone, haptics made from this material would not promote the fibrosis necessary to anchor the haptics to the surrounding tissue. This may lead to poor fixation and consequent migration or dislocation of the IOL.